In the Does Graphic Design have a low voting problem? the wording of "Intermediate Professional Designers" helped me realize this. Who are "Intermediate Professional Designers"?
Then I began researching StackExchange - Area51 to find where these intermediate users might be hiding.
Most of these should be completely closed in my opinion as being part of our Q&A already. Color-science should be split between us and Cogsci depending on the individual scope of the question. Marketing is more difficult but in my opinion questions like "Is a marketing degree crucial for a job in an ad agency?", "Is print advertising really dead?" and "When can I find (online) great photos for my marketing campaign?" Can go in ours. I know most of the designs that get submitted to me come from a marketing person because I work in budget advertising where companies can't afford a marketer and a graphic designer.
Especially as we look to broaden our user base I think these are things we need to be looking into. Both to make sure that questions we can answer are redirected to us as the only one close to being a full site, and to make sure people know we exist rather than creating new proposals for every little thing.